Photographic processes using silver halide have been most widely used in the past for general photographic purposes, due to their excellent photographic properties such as sensitivity, control of gradation, etc., as compared with other photographic processes, such as an electrophotographic process or a diazo photographic process. In recent years, with respect to image formation processes for light-sensitive materials using silver halide, many techniques capable of easily and quickly obtaining images have been developed by changing from the conventional wet process using a developing solution to a dry development process, such as a process using heat, etc.
Heat-developable light-sensitive materials are known in the field of these techniques. Heat-developable light-sensitive materials and processes therefor have been described, for example, in Shashin Kogaku no Kiso (The Foundation of Photographic Technology), pages 553 to 555 (published by Corona Co., 1979); Eizo Jyoho (The Image Information), page 40 (April, 1978), Neblette's Handbook of Photography and Reprography, 7th Ed., pages 32 to 33 (Van Nostrand Reinhold Company), U.S. Pat. Nos. 3,152,904, 3,301,678, 3,392,020 and 3,457,075, British Pat. Nos. 1,131,108 and 1,167,777, and Research Disclosure, No. 17029, pages 9 to 15 (June, 1978).
Many different processes for obtaining color images have been proposed. With respect to processes for forming color images by the reaction of an oxidation product of a developing agent with a coupler, it has been proposed to use a p-phenylenediamine type reducing agent and a phenolic coupler or an active methylene coupler as described in U.S. Pat. No. 3,531,286, a p-aminophenol type reducing agent as described in U.S. Pat. No. 3,761,270, a sulfonamidophenol type reducing agent as described in Belgian Pat. No. 802,519 and Research Disclosure, pages 31 and 32 (September, 1975), and the combination of a sulfonamidophenol type reducing agent and a 4-equivalent coupler as described in U.S. Pat. No. 4,021,240.
Also, processes for forming a positive color image by a heat-sensitive silver dye bleach process, and useful dyes and methods for bleaching have been described, for example, in Research Disclosure, No. 14433, pages 30 to 32 (April, 1976), ibid., No. 15227, pages 14 and 15 (December, 1976), U.S. Pat. No. 4,235,957, etc.
Further, processes for forming-images upon heat-development utilizing compounds having a dye moiety and capable of releasing a mobile dye in correspondence or countercorrespondence to the reduction reaction of silver halide to silver under condition of high temperature have been described, for example, in European Patent Published Application Nos. 76,492 and 79,056, Japanese Patent Application (OPI) Nos. 28928/83, 26008/83, etc. (the term "OPI" as used herein refers to a "published unexamined Japanese patent application").
With these heat-developable light-sensitive materials the development is conducted by heating. However, light-sensitive materials once heated to a high temperature take much time to decrease their temperature, tending to result in overdevelopment and deterioration of the image quality. Further, it is possible for development proceeding to occur beyond a level, depending on subtle variations in conditions such as ambient temperature, heating temperature, moisture content of the light-sensitive material, time for heating, etc., even when the same pattern of heating is employed.
In order to eliminate such phenomena, it has been proposed to use compounds which react with alkalis to release development stopping agents as described in U.S. Pat. No. 4,009,029, and acid polymers for neutralization as disclosed in Research Disclosure, Vol. 123, page 22 and Vol. 180, page 18030 and British Pat. No. 2,082,787A. In heat-developable light-sensitive materials, however, the former do not effectively stop development, and the latter cause a reduction in the density of the image obtained because the bases are rapidly neutralized.
The most effective development-stopping means conceivable is to perform development in the presence of a compound which releases an acid at an appropriate time during development to neutralize the base which promotes development, thus stopping development. Very few compounds are known, however, which release acids when heated. For example, Japanese Patent Application (OPI) Nos. 58642/74 and 57452/75 describe acid components which at a temperature of at least 60.degree. C. are dissolved, or release volatile acids. Since, the compounds disclosed in these patent applications neutralize the bases before heat development is started, development is inhibited and the density of the images obtained is reduced.